Regex to Match 12-Hour Time Format

This regex validates times in the 12-hour format with AM/PM designation. Here is the token-by-token breakdown:

^ — Anchors the match at the start of the string.

(?:0?[1-9]|1[0-2]) — A non-capturing group matching valid hours (1-12). 0?[1-9] matches hours 1-9 with an optional leading zero (so both '2' and '02' are valid). 1[0-2] matches hours 10-12.

: — Matches a literal colon separating hours from minutes.

[0-5]\d — Matches valid minutes (00-59). The first digit is restricted to 0-5 and the second can be any digit.

(?::[0-5]\d)? — An optional non-capturing group matching seconds. When present, it starts with a colon followed by valid seconds (00-59). Many time displays omit seconds.

\s? — Matches an optional whitespace character between the time and the AM/PM designator. Some formats include a space (2:30 PM) while others do not (2:30PM).

[AaPp][Mm] — Matches the AM/PM designator. The first character class allows A or a and P or p, while the second allows M or m. This accepts AM, am, PM, pm, Am, Pm, and other case combinations.

$ — Anchors the match at the end of the string.

This pattern is commonly used for validating user input in scheduling applications, alarm clocks, and booking systems that use the 12-hour clock convention prevalent in the United States and several other countries.